1. Field of the Invention
The present invention relates to an oil filter apparatus for use in conjunction with an internal combustion engine. More particularly, the present invention relates to an oil filter apparatus including both a mechanically active filter element and a chemically active filter element incorporated therein. Even more particularly, the present invention relates to an oil filter of the type described, in which a chemically active filter element includes pellets formed of a basic conditioner intermixed with a polymeric binder, for counteracting acidic combustion products in engine oil.
2. Description of the Background Art
Many different types of fluid filters are known. Most such filters use a mechanical or ‘screening’ type of filtration, with a replaceable cartridge having a porous filter element therein.
In the oil filtration art, it is well known that normal operation of an internal combustion engine, particularly a diesel engine, results in the formation of contaminants. These contaminants include, among others, soot, which is formed from incomplete combustion of the fossil fuel, and acids that result from combustion. Both of these contaminants are typically introduced into the lubricating oil during engine operation, and tend to increase oil viscosity and to generate unwanted engine deposits, leading to increased engine wear.
The conventional solution to these problems has been to place various additives into lubricating oils. In order to combat soot-related problems, many conventional lubricating oils include dispersants that resist agglomeration of soot therein. These work well for a short period, but may become depleted. Additionally, due to the solubility and chemical stability limits of these dispersants in the oil, the service lives of the lubricating oil and the oil filter are less than optimal.
For combating combustion acid related problems, many conventional systems include neutralizing additives known as over-based detergents. These are a source of TBN (total base number), which is a measure of the quantity of the over-based detergent in the oil. The depletion of the TBN is an important limiting factor for many internal combustion engines, and in particular for heavy-duty applications with diesel engines.
In order to improve engine protection and to combat other problems, conventional lubricating oils often include one or more further additives, which may be corrosion inhibitors, antioxidants, friction modifiers, pour point depressants, detergents, viscosity index improvers, anti-wear agents, and/or extreme pressure additives. The inclusion of these further additives may be beneficial; however, with conventional methods, the amount and concentration of these additives are limited by the ability of lubricating oils to suspend these additives, as well as by the chemical stability of these additives in the oil.
Other solutions have been proposed in addition to the conventional method of mixing additives with lubricating oil. For example, in order to combat the build up of sludge in oil, U.S. Pat. No. 5,478,463, issued in 1995 to Brownawell et al, and entitled Method of Reducing Sludge and Varnish Precursors in Lubricating Oil; and U.S. Pat. No. 5,042,617, issued in 1991 to Brownawell, and entitled Method of Reducing the Presence of Sludge in Lubricating Oils, each disclose an oil filter and method for reducing the amount of sludge in lubricating oil as it circulates throughout an engine. These Brownawell patents provide for the inclusion of particles in an oil filter that are oil insoluble and oil wettable, and which complex with sludge such that at least some of the sludge that these particles come into contact with is immobilized on the particles. The Brownawell '617 patent discloses the inclusion of oil insoluble and oil wettable particles in an oil filter that are retained on a pelletized substrate, whereas the Brownawell '463 patent discloses the inclusion of such particles that are not retained on a substrate, but are nonetheless retained in the oil filter.
Another Brownawell patent, which relates to the reduction of combustion acids in lubricating oil, is U.S. Pat. No. 5,069,799 issued in 1991 and entitled Method For Rejuvenating Lubricating Oils. This Brownawell patent discloses an oil filter and method for reducing the amount of combustion acids in lubricating oil. In particular, it discloses a method of rejuvenating lubricating oil, which includes reduction of combustion acids, by serially passing the oil through first a chemically active filter media, then a physically active filter media, and finally an inactive filter media. In this '799 patent, the chemically active filter media includes a strong base, to displace weak bases that have combined with combustion acids. The combustion acid and the strong base then combine to form a salt, which is then physically trapped by subsequent mechanical filter media.
U.S. Pat. No. 5,225,081 to Brownawell discloses method of removing polynuclear aromatics from used lubricating oil. The method of the Brownawell '081 reference involves passing oil through a staged oil filter system, which may include a chemically active filter media. The chemically active filter media is made of a composite material including particles of an active component and a and a thermoplastic binder, which are a product of a heated extrusion process. Basic conditioners are given as one example of materials suitable for use as materials usable as chemically active filter media. Activated carbon is also emphasized as a preferred component of the filter media.
Some designs for multiple stage oil filters are known, such as those disclosed in U.S. Pat. Nos. 4,557,829 and 4,886,599. U.S. Pat. No. 4,886,599 to Bachmann et al. discloses a filter cartridge with sequential concentric cylindrical filter elements, for both chemical and mechanical filtration of oil contained in an oil-sealed vacuum pump.
Other designs for oil filters that contain extra additives and dispense those additives into oil, over time, are disclosed in U.S. Pat. Nos. 4,075,098 and 5,552,040.
A need still exists in the art for an improved oil filter having a basic conditioner incorporated therein to counteract the effects of acidic combustion products in the oil. A need also exists for an improved oil filter which could extend the useful life of engine oil, so as to allow a user to extend the time interval between oil changes in a vehicle, particularly a vehicle having a diesel engine.